Earth's tropics are hotter than the polar regions for a good reason, so scientists are puzzled that the same pattern doesn't show on Jupiter's moon Io.

A new map of Io's nighttime surface temperatures comes from NASA's Galileo spacecraft. Aside from hot spots at volcanic sites, night temperatures on Io appear to be about the same near the equator as near the poles even though, as on Earth, the equator gets more direct sunshine to heat the surface.

The Io temperature map is available online at http://www.jpl.nasa.gov/images/io , and a new, enhanced-color Galileo image of Europa's icy surface is available at http://www.jpl.nasa.gov/images/europa. The Europa image proved useful in a study of the age of that moon's surface by Dr. Cynthia Phillips of the SETI Institute, Mountain View, Calif. Captions are posted with the images.

Some 250 scientists meet June 24-30 in Boulder, Colo., to discuss Io, Europa and other members of the Jupiter system. Dr. John Spencer, of the Lowell Observatory, Flagstaff, Ariz., will describe some possible explanations for Io’s odd heat balance. For example, the poles may have more volcanic heating than the lower latitudes, or they may be surfaced with materials that cool off slower at night.